Binding of a Phosphorylated Inhibitor to Ribulose Bisphosphate Carboxylase/Oxygenase during the Night.
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Journal: 2010/June - Plant Physiology
ISSN: 0032-0889
PUBMED: 16664337
Abstract:
The activity of ribulose-1,5-bisphosphate carboxylase/oxygenase was measured at various times during the purification of the enzyme from leaves of Nicotiana tabacum which were collected either 1 hour before the start of the photoperiod (predawn) or in the middle of the photoperiod (midday). The activity of the enzyme in extracts of the predawn leaves (0.8 units/mg enzyme) was consistently about 2-fold lower than that measured in extracts of midday leaves (1.7 units/mg enzyme). The activity of the predawn enzyme was increased to that of the midday enzyme following removal of CO(2) and Mg(2+) (deactivation), (NH(4))(2)SO(4) precipitation, or incubation in SO(4) (2-) (18 millimolar required for one-half maximal increase). Following purification to >95% homogeneity, the predawn enzyme was found to have approximately 0.5 moles of bound organic phosphate per mole of enzyme active sites, while the midday enzyme had only approximately 0.08 moles of bound organic phosphate per mole of enzyme active sites. Deactivation of the predawn enzyme or treatment with 0.2 molar SO(4) (2-) resulted in the removal of most of the bound organic phosphate. These findings support the hypothesis that following the night period about 50% of the enzyme is catalytically inactive because of the tight-binding of a small molecular weight, phosphorylated inhibitor at the active site.
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Plant Physiol 78(4): 839-843
PMID: 16664337

Binding of a Phosphorylated Inhibitor to Ribulose Bisphosphate Carboxylase/Oxygenase during the Night <sup><a href="#fn1" rid="fn1" class=" fn">1</a></sup>

Abstract

The activity of ribulose-1,5-bisphosphate carboxylase/oxygenase was measured at various times during the purification of the enzyme from leaves of Nicotiana tabacum which were collected either 1 hour before the start of the photoperiod (predawn) or in the middle of the photoperiod (midday). The activity of the enzyme in extracts of the predawn leaves (0.8 units/mg enzyme) was consistently about 2-fold lower than that measured in extracts of midday leaves (1.7 units/mg enzyme). The activity of the predawn enzyme was increased to that of the midday enzyme following removal of CO2 and Mg (deactivation), (NH4)2SO4 precipitation, or incubation in SO4 (18 millimolar required for one-half maximal increase). Following purification to >95% homogeneity, the predawn enzyme was found to have ∼0.5 moles of bound organic phosphate per mole of enzyme active sites, while the midday enzyme had only ∼0.08 moles of bound organic phosphate per mole of enzyme active sites. Deactivation of the predawn enzyme or treatment with 0.2 molar SO4 resulted in the removal of most of the bound organic phosphate. These findings support the hypothesis that following the night period about 50% of the enzyme is catalytically inactive because of the tight-binding of a small molecular weight, phosphorylated inhibitor at the active site.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.
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Department of Biology, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061
Supported by grants from the United States Department of Agriculture/Competitive Research Grants Office (84-CRCR-1-1511) and the Virginia Agricultural Experiment Station (Hatch Project 612459).
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Abstract
The activity of ribulose-1,5-bisphosphate carboxylase/oxygenase was measured at various times during the purification of the enzyme from leaves of Nicotiana tabacum which were collected either 1 hour before the start of the photoperiod (predawn) or in the middle of the photoperiod (midday). The activity of the enzyme in extracts of the predawn leaves (0.8 units/mg enzyme) was consistently about 2-fold lower than that measured in extracts of midday leaves (1.7 units/mg enzyme). The activity of the predawn enzyme was increased to that of the midday enzyme following removal of CO2 and Mg (deactivation), (NH4)2SO4 precipitation, or incubation in SO4 (18 millimolar required for one-half maximal increase). Following purification to >95% homogeneity, the predawn enzyme was found to have ∼0.5 moles of bound organic phosphate per mole of enzyme active sites, while the midday enzyme had only ∼0.08 moles of bound organic phosphate per mole of enzyme active sites. Deactivation of the predawn enzyme or treatment with 0.2 molar SO4 resulted in the removal of most of the bound organic phosphate. These findings support the hypothesis that following the night period about 50% of the enzyme is catalytically inactive because of the tight-binding of a small molecular weight, phosphorylated inhibitor at the active site.
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